Patent foramen ovale (“PFO”) is an anatomical interatrial communication with potential for right-to-left shunting of blood. Specifically, PFO is a flap-like opening between the atrial septa primum and secundum of the heart that persists after one year of age. In utero, the foramen ovale serves as a physiologic conduit for right-to-left shunting of blood in the fetal heart. After birth, with the establishment of pulmonary circulation, the increased left atrial blood flow and pressure presses the septum primum against the walls of the septum secundum, covering the foramen ovale and resulting in functional closure of the foramen ovale. This closure is usually followed by anatomical closure of the foramen ovale due to fusion of the septum primum to the septum secundum.
If anatomical closure of the foramen ovale does not occur, a patent foramen ovale is created. A PFO results when either partial or no fusion of the septum primum and the septum secundum occurs. In the case of partial or no fusion, a persistent passageway or PFO track exists between the septum primum and the septum secundum. The passageway is typically parallel to the plane of the septum primum, and has a mouth that is generally oval in shape. Normally, the passageway is long and quite narrow. Because the mean left atrial pressure is typically higher than the mean right atrial pressure, the opening is usually held closed. However, at times, the mean right atrial pressure may exceed the mean left atrial pressure, causing the PFO track to open and allow the passage of blood (and possible blood clots) from the right atrium to the left atrium (and into systemic circulation). Although the PFO track is often held closed, the endothelialized surfaces of the tissues forming the PFO track prevent the tissues from healing together and permanently closing the PFO track.
Studies have shown that a relatively large percentage of adults have a patent foramen ovale. It is believed that embolism via a PFO may be the cause of a significant number of ischemic strokes, particularly in relatively young patients. Such paradoxical embolism via PFO is considered in the diagnosis of patients who have suffered a stroke or transient ischemic attack (“TIA”) in the presence of a PFO and without another identified cause of ischemic attack. Blood clots that form in the venous circulation can embolize, and may enter the arterial circulation via the PFO, subsequently entering the cerebral circulation, resulting in an embolic stroke. Blood clots may also form in the vicinity of the PFO, and embolize into the arterial circulation and into the cerebral circulation. Patients suffering a cryptogenic stroke or TIA in the presence of a PFO are often considered for medical therapy to reduce the risk of a recurrent embolic event. Pharmacological therapy often includes oral anticoagulants or antiplatelet agents to block the formation of emboli. If pharmacotherapy is unsuitable, open heart surgery may be employed to close a PFO with stitches, for example. Like other open surgical procedures, this surgery is highly invasive, risky, requires general anesthesia, and may result in a lengthy recuperation.
Nonsurgical closure of a PFO is possible with umbrella-like devices and a variety of similar mechanical closure devices originally developed for percutaneous closure of atrial septal defects (“ASD”), a condition where the septum primum is often under-developed and perforated. Many of the devices used for closure of an ASD, however, are often technically complex to manufacture and assemble, have a high septal profile, are difficult to deploy to a precise location, and are difficult to implant without deforming the atrial septa and PFO track. In addition, such devices may be difficult or impossible to reposition or retrieve in cases where the original positioning was unsatisfactory. Moreover, these devices are specially designed to close ASDs, or hole-like defects, and therefore are not optimally designed to close and seal a PFO, an overlapping, flap-like, passageway defect. Thus, when inserting an ASD device to close a PFO, the narrow opening and thin flap may form impediments to proper deployment of the device, resulting in residual leakage through the PFO. Even if an occlusive seal is formed, the device may be deployed in the PFO track at an angle, leaving some components insecurely seated against the septum and thereby increasing the risk of thrombus formation due to hemodynamic disturbances.
Accordingly, there exists a need for instrumentation and techniques that facilitate more effective and efficient closure of aberrant, flap-like bodily openings such as patent foramen ovales.